If not using the xarray backend, in some situations the kwargs["_xarray_backend"] throws a KeyError. Fixed that if not available, setting to False, which is the default.
If opening a GRIB v1 file, there was an AssertionError which is changed to raise an error and offer an error message.
Removed an unnecessary if block that tested for a header which is now done in a loop immediately before.
If not using the xarray backend, in some situations the kwargs["_xarray_backend"] throws a KeyError. Fixed that if not available, setting to False, which is the default.
If opening a GRIB v1 file, there was an AssertionError which is changed to raise an error and offer an error message.
Removed an unnecessary if block that tested for a header which is now done in a loop immediately before.